Counting Atoms and Balancing Equations

TRUE or FALSE? A compound is always molecule: A molecule is always a compound

Example 1 – Sulfuric Acid O Number of Molecules: Atoms H: O: S: S O O H H2SO4 H O These are subscripts (small numbers). They indicate the quantity of the atom that appears immediately before the number.

Example 2 – Calcium hydroxide Number of Molecules: Atoms Ca: O: H: Ca O O H Ca(OH)2 H Sometimes a subscript will appear after brackets. This means that all the atoms inside the brackets are multiplied by this number.

Example 3 – Calcium hydroxide… again 3 Ca(OH)2 Ca O H This is a coefficient. When a coefficient appears before a molecule, it tells you how many of these molecules there are. Multiply ALL atoms in the molecule by this coeffcient.

Example 3 – Calcium hydroxide… again 3 Ca(OH)2 Ca O H Number of Molecules: Atoms Ca: O: H:

Ca3(PO4)2 Al2(SO4)3 4 Mg(NO3)2 Try these… Calcium phosphate Aluminum sulfate 4 molecules of Magnesium nitrate Ca3(PO4)2 Al2(SO4)3 4 Mg(NO3)2

Balancing Equations In a chemical reaction, atoms are rearranged. The number of atoms in the reactants MUST EQUAL the number of atoms in the products. This is the Law of Conservation of Matter: Matter is neither created nor destroyed. It is merely rearranged.

Reactants of cellular respiration H O

Products of cellular respiration H O

Complete p. 14-15